The present invention relates to a Lysholm compressor, and in particular, to a Lysholm compressor which preferably supplies compressed air to a fuel cell.
As a conventional Lysholm compressor, there is the screw type air compressor which is disclosed in Japanese Patent Application Laid-Open Publication No. H7-233730, shown in FIG. 11.
The screw type air compressor shown in FIG. 11 is, specifically, a Lysholm compressor for pressure charging for an engine. When a discharge pressure required of the compressor is low, a spool valve 101 is opened, and the air which is in the process of being compressed is bypassed from a tooth groove space 105 (which will be necessarily called a xe2x80x9crotor tooth groove spacexe2x80x9d hereinafter) of a rotor 103, via a bypass path 107 to a discharge port 109. When the discharge pressure required of the compressor is high, the spool valve 101 is closed, and the compressed air is prevented from flowing backward from the discharge port 109 via the bypass path 107 to the rotor tooth groove space 105. In this way, a high efficiency is obtained over a wide range of pressures.
Note that, in FIG. 11, reference numeral 111 denotes a housing in which the rotor 103 is provided, reference numeral 113 denotes a suction port, reference numeral 115 denotes sucked-in air which is sucked in from the suction port 113, and reference numeral 117 denotes discharged air (compressed air) which is discharged from the discharge port 109.
However, according to studies of the present inventor, in a case in which such a conventional Lysholm compressor is used for a fuel cell, and specifically, as a compressor for a fuel cell, the following situation may occur.
Namely, a range of pressures required of a compressor for a fuel cell is very wide, from low pressures to high pressures. In particular, with regard to pressures at the high pressure side, although a pressure-charging pressure for an engine is less than or equal to 80 kPaG, a pressure-charging pressure for a fuel cell is greater than or equal to 200 kPaG which is extremely high. Because the temperature of the compressed air at this time rises to a high temperature of greater than or equal to 200xc2x0 C. at maximum, the compressor for a fuel cell is run in an extremely wide range of temperatures from low temperatures to high temperatures.
However, the spool valve 101 must be sealable. Therefore, the clearance between the spool valve 101 and the bypass path 107 is extremely narrow. Thus, in a case, such as that of a compressor for a fuel cell, in which the compressor is used in an extremely wide temperature range, it is easy for so-called biting-in to occur, i.e., it is easy for the spool valve 101 to catch on corresponding slide portions to scratch them. Thus, the reliability of the operation of the valve deteriorates.
Further, because there are cases in which the fuel cell is affected by oil, the spool valve 101 cannot be lubricated sufficiently by oil. Thus, the reliability of the operation of the valve deteriorates even more.
The present invention was done in consideration of the above-described studies, and an object of the present invention is to provide a Lysholm compressor for a fuel cell which can obtain high efficiency in a wide range of pressures from low pressures to high pressures and can carry out highly reliable operation, without using an additional valve element such as a spool valve or the like.
In order to achieve the above-mentioned object, a Lysholm compressor of the present invention is provided with: a rotor, in which a spiral tooth groove is formed in order to form a tooth groove space, taking-in and compressing a fluid in the tooth groove space; a discharge port which discharges the fluid compressed by the rotor; a bypass path which communicates the discharge port and the tooth groove space; and an outlet portion of the bypass path which faces the discharge port. Here, the outlet portion is a pipe shape which projects out into the discharge port, and an outer peripheral portion of an end portion of the pipe-shaped bypass path outlet portion is tapered so as to become more narrow toward a distal end thereof.
In other words, a Lysholm compressor of the present invention is provided with: a rotor, in which a spiral tooth groove is formed in order to form a tooth groove space, taking-in and compressing a fluid in the tooth groove space; a discharge port which discharges the fluid compressed by the rotor; a bypass path which communicates the discharge port and the tooth groove space; and acontracted flow forming means, which is provided at an outlet portion of the bypass path which faces the discharge port, and which forms a contracted flow of fluid which flows from the discharge port toward the tooth groove space in the bypass path.
Other and further features, advantages, and benefits of the present invention will become more apparent from the following description taken in conjunction with the following drawings.